It is well known that olefins such as ethylene, propylene and 1-butene can be polymerized in the presence of certain metallic catalysts, particularly the reaction products of organometallic compounds and transition metal compounds, to form substantially linear polymers of relatively high molecular weight. Typically such polymerizations are carried out at relatively low temperatures and pressures.
It has been proposed to use certain organolanthanide compounds as olefin polymerization catalysts. Ballard et al in J.C.S. Chem. Comm., (1978) pages 994 and 995 reported that certain alkyl bridged complexes of lanthanide metals such as [(C.sub.5 H.sub.5).sub.2 ErCH.sub.3 ].sub.2 and [(C.sub.5 H.sub.4 R).sub.2 YCH.sub.3 ].sub.2, would polymerize ethylene. Marks and Mauermann in their U.S. Pat. No. 4,668,773 disclose that an ethylene polymerization catalyst could be obtained by reacting an anionic pentamethylcyclopentadienyl lanthanide halide lithium ether complex with a special type of lithium alkyl and then reacting that product with hydrogen to yield a catalyst of the general [(C.sub.5 Me.sub.5).sub.3 LnH].sub.2. The dimeric hydrido complex of Marks et al was reported to have activities as high as 3,000 grams of polyethylene per millimole Nd, however, the data also indicates that the catalyst had a very short lifetime (on the order of seconds to minutes). The overall productivity of the catalyst was thus quite low. The synthesis of this catalyst system was also very complex. It was a multi-step procedure that had to be carried out under rigorously anaerobic conditions. The procedure also requires the use of exotic organolithium compounds which contain no beta hydrogen or beta alkyl groups.
An object of the present invention is to provide a process under which anionic organolanthanide complexes of the type described in the Marks et al patent could be made directly active to olefin polymerization by using simple metal alkyls.
Other aspects, objects, and advantages of the present invention will be apparent from the following disclosure.